Capacitor is the passive component that store electricity and electrical energy. Its capacitance refers to the storage of free charge at a given potential difference. Under normal circumstances, charges will be moved by force in an electric field. When there is a medium between conductors, it will hinder the movement of charges and accumulate on the conductors. The amount of stored charge is called capacitance.

As one of the three basic passive devices, capacitors have been widely used in the fields of electronics and power.

Common types of capacitors include ceramic capacitors, aluminum electrolytic capacitors, and tantalum capacitors.

Previous article: Types of Capacitors and its applications

Capacitor in the Electronic Circuits

In a DC circuit, a capacitor is equivalent to an open circuit. The simplest capacitors are constructed with plates at both ends and an insulating dielectric in between. Under the premise that the critical voltage (breakdown voltage) of the capacitor is not exceeded, the electrode plate is charged to form a voltage after energization, but due to the insulating material in the middle, the entire capacitor is non-conductive.

However, when the voltage across the material increases to a certain extent, the material can conduct electricity, and we call this voltage the breakdown voltage. After the capacitor is broken down, it is not an insulator.

A purely capacitive AC circuit is a circuit that contains only an AC power source and a capacitor, with the capacitor connected directly across the AC power supply voltage. Capacitors charge and discharge as the supply voltage increases and decreases. Current will flow through the circuit first in one direction and then in the other direction. Actually no current flows through the capacitor. Electrons build up on one plate and are expelled from the other plate in rapid successions, like a current flowing through an insulator separating the plates.

Since it is an energy storage element, it can also be discharged, so what is the difference between it and a battery? Capacitors use energy storage and instantaneous charging and discharging characteristics to work in the circuit, and can play the role of filtering, rectifying, blocking DC and AC, etc. The way to store charge is to store the charge directly on the electrode plate, while the battery stores it by chemical energy and can discharge stably for a long time.

Ceramic Capacitors

The Parameters Should be Taken Into Consideration When Selecting a Capacitor

The main parameters of capacitors are nominal capacity and allowable deviation, rated working voltage, insulation resistance, temperature coefficient, capacitor loss and frequency characteristics.

Nominal Value of Capacitance (C)

The capacitance marked on the capacitor is called the nominal capacitance. There is a certain deviation between the actual capacity of the capacitor and the nominal capacity. The allowable maximum deviation range between the nominal capacity and the actual capacity of the capacitor is called the allowable deviation of the capacitor. The error between the nominal capacity of the capacitor and the actual capacity reflects the accuracy of the capacitor.

Rated Voltage (V)

The rated working voltage refers to the highest point voltage at which the capacitor can work continuously and reliably within the specified temperature range, and is sometimes divided into rated DC working voltage and rated AC working voltage. The rated working voltage is related to the medium used by the capacitor and the ambient temperature. The ambient temperature is different, and the maximum working voltage that the capacitor can withstand is also different.

Temperature Coefficient

Changes in temperature can cause small changes in the capacitance of capacitors, and the temperature coefficient is usually used to express this characteristic of capacitors. The temperature coefficient refers to the relative change in the capacitance of the capacitor when the temperature changes by 1ºC within a certain temperature range.

Leakage Current

The dielectric of the capacitor is not absolutely insulating, and there will always be some leakage, resulting in leakage current. Generally, the leakage current of electrolytic capacitors is relatively large, and the leakage current of other capacitors is very small. When the leakage current is large, the capacitor will heat up; when the heat is serious, the capacitor will be damaged due to overheating.

Insulation Resistance

The value of the insulation resistance of a capacitor is equal to the ratio of the voltage applied across the capacitor to the leakage current through the capacitor. For capacitors of the same medium, the larger the capacitance, the smaller the insulation resistance. The size and change of the insulation resistance of capacitors will affect the working performance of electronic equipment. For general electronic equipment, the larger the insulation resistance, the better.

Frequency Characteristics

Frequency characteristics refer to the performance of capacitors for various frequencies. Capacitors with different dielectric materials have different maximum operating frequencies.

Dielectric Loss

The energy consumed by the capacitor under the action of the electric field is usually expressed by the ratio of the lost power to the reactive power of the capacitor, that is, the tangent of the loss angle. The larger the loss angle, the greater the loss of the capacitor, and the capacitor with a larger loss is not suitable for working at high frequencies.